The overall goal of this research project is to further elucidate the cognitive deficit or deficits responsible for the reading and spelling difficulties of individuals with familial dyslexia. This project is unique among studies of dyslexia in that the dyslexic subjects are homogeneous with respect to etiology: they have an autosomal dominant form of familial dyslexia which is linked to chromosome 15. Thus they are likely to be both more homogeneous and specific in their phenotype than other dyxlexic populations. Moreover, as in the case of other cognitive disorders (e.g., mental retardation), the identification of an etiologically pure subtype (e.g., Down's Syndrome) has significant long term advantages in terms of both understanding the pathophysiological mechanisms involved and prevention. Since our previous work indicates that the nature of these dyslexics' reading and spelling problems changes with development, the present study will also attemtp to further specify the basis of these developmental changes. The first phase of the investigation will focus on developing experimental paradigms to test competing hypotheses of what the underlying cognitive deficit or deficits are at three different developmental ages: adulthood, 11 to 14 years, and 7 to 10 years. In the second phase, these paradigms will then be applied cross-sectionally to samples of familial dyslexics, their unaffected family members, and non-familial dyslexics in each age group. A third phase will involve a three year longitudinal study of the youngest group in all three categories of subjects. A long-term goal is to use the understanding of the reading and spelling deficits in this particular subtype of dyslexia to improve diagnosis and intervention for other learning disabilities.